This invention relates to systems for carrying cargo in aircraft. This invention relates in particular to systems for carrying cargo in passenger aircraft This invention also relates to methods for converting passenger aircraft to cargo use and then converting the aircraft back to passenger use.
In the usual practice, aircraft are built in passenger carrying versions and cargo-carrying versions Cargo aircraft and passenger aircraft are separately certified by the Federal Aviation Administration in the United States.
It is known in the prior art to convert passenger carrying aircraft to cargo-carrying aircraft. This process, as performed in the prior art, is both time-consuming and expensive. The process requires, initially, removal of all the interior appurtenances such as seats, restrooms, overhead luggage racks, and galleys of the passenger aircraft In order to meet Federal Aviation Administration ("FAA") requirements that there be structures to restrain cargo from moving into the crew cabin under an acceleration of 9g's, it is conventional to install a net or barrier between the cargo area and the crew cabin of an aircraft that has been converted from passenger to cargo use. This process requires removal of a portion of the interior skin of the aircraft and attachment of stringers to the interior structural members of the aircraft so as to provide anchor points for the net or barrier. Furthermore, it is conventional to remove the floor of the passenger aircraft, install reinforced support members and put in a stronger floor. Because of the permanent nature of these changes, it is rarely desirable to return the aircraft to passenger service once this process has been carried out.
It will be noted that, where an FAA requirement relating to acceleration is expressed as a specified number of times the acceleration of gravity the FAA in fact requires an additional factor of 15 percent All references to FAA requirements so expressed on this application should be so understood
An example of a passenger aircraft that has been converted to cargo use is given in Wiseman. et al., U.S. Pat. No. 4,747,504, the disclosure of which is expressly incorporated by reference herein. Use of a passenger aircraft according to the teachings of Wiseman et al. would require numerous changes to the aircraft. The installation of a net or barrier forward of the cargo section of the aircraft which, as noted above, is expensive and time-consuming and makes conversion of the aircraft back to passenger use uneconomical, is required Furthermore, removal of all of the interior appurtenances of the aircraft including seats, seat tracks, galleys, lavatories, luggage racks, and window reveals, is necessary. Installation of a set of guide rails on the floor of the aircraft passenger cabin is necessary. Moreover, FAA certification requirements for passenger aircraft require an aisle down the center of an aircraft. The Wiseman, et al. cargo container is too large to permit such an aisle. Indeed, in the Wiseman, et al. central portion of the cabin of an aircraft is occupied by a central guide rail. Accordingly, an aircraft employing the Wiseman et al. system must be certified by the FAA as a cargo aircraft, further adding to the cost and delay of the conversion process.
Conventional cargo aircraft also have substantially different fire detection and extinguishing systems from passenger aircraft. Cargo aircraft have smoke detectors in the cargo area of the aircraft and separate air circulation and purification systems in the crew cabin and cargo area. When the smoke detectors in the cargo area detect smoke, the air circulation is shut down in the cargo area, extinguishing the fire. Fassenger aircraft, by contrast, have a single air circulation system. Thus, pursuant to FAA requirements, cargo must either be stored in containers which are so constructed that a fire in such a container will extinguish itself within a brief period, or the aircraft must have onboard fire-fighting equipment. As a result, if a passenger aircraft were used with the Wiseman et al. system, extensive modifications would have to be carried out to the air circulation systems of the aircraft.
Moreover, passenger aircraft have viewports in the floor of the passenger cabin for viewing the landing gear. These viewports are required by the FAA as a back-up system if primary systems do not indicate that the landing gear are in proper position for landing. In order to use the viewports, crew members must walk from the crew cabin to the passenger cabin. In modifying a passenger aircraft to use the system of Wiseman et al.. the aisle is blocked by containers, making the viewports inaccessible. As a result, installation of an alternative system for verifying whether the landing gear are in position is required.
The carrying of cargo, particularly parcels and small packages, is a seasonal business. In the United States, the quantity of packages shipped increases enormously every year in December, and then promptly decreases in January. Accordingly, it is highly desirable for shippers of parcels and packages to obtain additional aircraft during the month of December, but not economical to maintain such aircraft throughout the year. Furthermore, in the passenger aircraft business, there are often a significant number of aircraft that are not in use for passenger service during December, which corresponds to the peak period for delivery of parcels and packages by air. As a result, there is a need for a method of quickly converting such excess passenger aircraft to use as cargo aircraft during the peak period, and rapidly converting them back to passenger use after such peak period would be desirable.